Paramagnetic substances can be magnetized under an external magnetic field. Paramagnetic materials include, for example, manganese, chromium, cerium, iron, cobalt, potassium, vanadium, and their oxides or sulfides. Without influence of the external magnetic field, the magnetic dipole in a paramagnetic molecule points in random directions, so it has zero magnetism. As a suitable external magnetic field is applied, a paramagnetic substance is magnetized since the number of magnetic dipoles aligned parallel toward the direction of the magnetic field is more than those aligned away from the field.
Conventional magnetic filters remove paramagnetic substances or particles from gas or liquid fluids through the influence of an external magnetic field generated by permanent magnetic or electromagnetic sources. For example, magnetic filters disclosed in U.S. Pat. No. 8,506,820 to Yen et al, U.S. Pat. No. 8,636,907 to Lin et al, and U.S. Pat. Nos. 8,900,449 and 9,080,112 both to Yen et al, can remove paramagnetic particles from liquid streams in refinery and chemical facilities. The paramagnetic particles which include FeS, FeO, Fe(OH)2, Fe(CN)6, etc. are formed when carbon steel, which is a common material in plant construction, corrodes in the presence of acidic contaminants in the process stream to yield ferrous ions, which react with sulfur, oxygen and water. These paramagnetic contaminants tend to adhere to magnets.
Diamagnetic substances contain pairs of magnetic dipoles which tend to cancel out the magnetism internally. Diamagnetic materials include, for example, carbon (diamond), carbon (graphite), silica, alumina, bismuth, phosphorous, mercury, zinc, lead, tin, copper, silver, gold, water, ethyl alcohol, etc. In the presence of an external magnetic field, the magnetic dipoles of diamagnetic substances align parallel and in reverse direction to the magnetic field and therefore exhibit no magnetism. Prior art magnetic filters cannot remove diamagnetic substances.
Filtration with mesh screens and the like is the standard employed to separate diamagnetic particles from gas or liquid fluids but this technique is not efficient for small particles. For example, nano carbon particles such as particulate matter PM 2.5 emitted from power plants, steel mills, and mobile sources including cars and motorcycles cannot be effectively abated. Similarly, nano particles in the form of catalyst fines, steel rust, carbon residue or polymerized slurry found in refinery and chemical plants cannot be effectively filtered. Solid particles comprising FeS, FeO, sand, carbon residue, etc. of various sizes are also present in natural gas processes. Paramagnetic and diamagnetic materials are major constituents of both natural and industrial pollutants and contaminants.
It is highly desirable to develop systems for removing both of paramagnetic and diamagnetic particles, or at least the diamagnetic particles, of all sizes from the gas and liquid fluids.